Sex differences Flashcards
Development of sex organs
- Start with same gonads -> sexual differentiation -> different male/female sex organs
Factors determining the development of male sex organs
SRY region on Y chromosome codes for testis-determining factor that binds to DNA in cells of undifferentiated gonads and causes them to become testes (father sperm)
Testes produce hormones that have defeminising (anti Mullerian hormone) and masculinising (androgen) effects
Anti-Mullerian hormone
A peptide secreted by fetal testes
Has defeminising effects, inhibits development of Mullerian system
Androgens (2 of them)
Testosterone
acts on androgen receptors in cells of Wolffian system and stimulates development into male internal sex organs
Dihydrotestosterone produced FROM testosterone by 5alpha reductase
Critical to stimulate development into male genitals
Testis determining factor
230 amino-acid long protein
Point mutations can prevent development of testes
Factors determining the development of female sex organs
By default, primordial sex organs develop into female sex organs
In the absence of testis-determining factor primordial gonads develop into ovaries.
In the absence of androgens produced by testes, internal and external sex organs develop into female organs (without any other hormonal influences necessary).
Recent discovery about the development of female sex organs
Wolffian system regression requires COUP-TFII, a nuclear receptor, so is not a passive process (A Swain, 2017, Science 357:648).
The genetic sex of a human fetus is determined by
The father’s sperm.
The prenatal development of female internal sex organs requires
No hormones at all
Abnormal development of sex organs
XY sex reversal
Androgen insensitivity syndrome
Turner’s syndrome
Persistent Mullerian duct syndrome
XY sex reversal
Point mutations in the SRY region of the Y chromosome result in female sex organs in XY individuals (see Werner et al, 1995, Cell 81 :705).
Androgen insensitivity syndrome
A condition caused by congenital lack of functioning androgen receptors; in a person with XY sex chromosomes, causes development of a female with testes but no internal sex organs
Turner’s syndrome
The presence of only one sex chromosome (an X chromosome) results in lack of ovaries but otherwise normal female sex organs and genitalia
Persistent Mullerian duct syndrome
Congenital lack of anti-Mullerian hormone causes the development of both male and female internal sex organs in an XY individual
primary sex characteristics
Gonads
internal and external sex organs
Secondary sex characteristics
- enlarged breasts
- widened hip
- facial hair
- deep voice
- sexual maturity
are not developed until puberty